WO2003093838A1

WO2003093838A1 - Flow velocity sensor

Info

Publication number: WO2003093838A1
Application number: PCT/JP2003/005473
Authority: WO
Inventors: Tarou Nakata; Shoji Kamiunten; Seishi Nakano
Original assignee: Yamatake Corporation
Priority date: 2002-05-02
Filing date: 2003-04-28
Publication date: 2003-11-13
Also published as: CN100405066C; JP3802443B2; JP2003322658A; CN1650175A

Abstract

A flow velocity sensor, comprising a base stand having a space part, a thin-film layer formed on the surface of the base stand where the space part is formed, a first temperature measuring resistance element and a second temperature measuring resistance element formed on the thin-film layer and connected in series to each other, a flow velocity calculation means for calculating the flow velocity of fluid based on a temperature difference between the first and second temperature measuring resistance elements, and a control means for controlling the first and second temperature measuring resistance elements so that the averaged temperature of the first and second temperature measuring resistance elements is always higher by a specified temperature than the ambient temperature.

Description

Description Flow velocity sensor Background of the invention

The present invention relates to a flow rate sensor used for measuring a flow rate of a fluid such as a gas or a liquid.

The applicant has proposed in Japanese Patent Application Laid-Open No. 2-2595277 a flow rate sensor having a semiconductor fine processing configuration realizing high accuracy and high speed response. The configuration of the flow velocity sensor disclosed in Japanese Patent Application Laid-Open No. 2255952/27 will be described with reference to FIGS. 6A and 6B.

The flow velocity sensor is formed on a base 1 made of single-crystal silicon or the like, and a void 2 is formed in the center of the base 1. On the base 1, a thin film layer 3 is formed which is spatially isolated from the base 1 by the gap 2. The thin film layer 3 is provided with a pair of slits 4 a and 4 b communicating with each other through the gap 2 at a predetermined interval. Further, between these slits 4a and 4b, there is provided a slit 5 extending in a direction orthogonal to a straight line connecting the slits 4a and 4b. Two arrangement parts 6a and 6b are formed between b. The disposition parts 6 a and 6 b are thermally insulated from each other by the slit 5.

A temperature measuring resistance element A 1 functioning as a heating element and a temperature sensor is formed in the disposing portion 6 a, and a temperature measuring resistance element B functioning as a heating element and a temperature sensor is similarly formed in the disposing portion 6 b. 1 is formed. Further, in the portion where the thin film layer 3 and the base 1 are in thermal contact with each other, that is, in the portion where the void portion 2 is not provided, an ambient temperature measuring resistance element C 1 whose resistance value changes with the ambient temperature is formed. Is done.

FIG. 7 is an electric circuit diagram of the flow velocity sensor proposed in Japanese Patent Application Laid-Open No. 2-259595. The electric circuit of the flow velocity sensor is for measuring the flow velocity of the gas moving on the base 1, and includes a temperature difference detection circuit 100, a constant current circuit 200, and a switching circuit 300. Be composed. The temperature difference detection circuit 100 is composed of a temperature measuring resistor element A1, B1 and a resistor R101, R102 having a larger resistance value. Circuit, an amplifier A101, A102 for amplifying the output voltage of the bridge circuit, a differential amplifier A103 for outputting a difference value between the output voltages of the amplifiers A101, A102, and resistors R103 to R109. Be composed. The bridge circuit is supplied with a constant current from a constant current circuit 200 composed of an ambient temperature resistance element C1, transistors TR201 and TR202, and a resistor R201, and is composed of a transistor T301 and a resistor R301. It is intermittently driven by the switching circuit 300 that is operated.

Here, the ambient temperature measuring resistance element C1 is provided to compensate for a change in the ambient temperature. The resistance temperature elements Al and B 1 generate heat by the constant current supplied from the constant current circuit 200. Here, since the resistances R101 and R102 have considerably larger resistance values than the resistance temperature measurement elements A1 and B1, it is assumed that the resistance temperature elements Al and B1 are driven by a constant current. Can be considered.

When the gas flows on the surface of the flow velocity sensor, the resistance temperature element A1 located on the upstream side is cooled more strongly than the resistance element B1 located on the downstream side. As a result, a temperature difference appears between the two resistance temperature measurement elements Al and B1, and this temperature difference becomes a resistance change, the bridge circuit loses its balance, and the difference amplifier A 103 responds to the temperature difference. Output voltage.

The flow velocity sensor proposed in Japanese Patent Application Laid-Open No. 2-259527 is capable of detecting the flow velocity of a fluid with high accuracy because the resistance X-elements Al and B 1 are formed on the thermally insulated thin film layer 3. Has features. However, in this flow velocity sensor, when the flow velocity increases, the amount of heat energy taken from the downstream resistance temperature measuring element B 1 increases and the temperature decreases, and the upstream and downstream resistance temperature elements A 1, B 1 The difference in resistance value of 1 decreases. For this reason, in the flow velocity sensor proposed in Japanese Patent Application Laid-Open No. 2-259527, there is a problem that, when the flow velocity is increased, the sensitivity is reduced and measurement at a high flow velocity becomes difficult. In this flow velocity sensor, the temperature measurement resistance elements Al and B 1 are driven by a constant current, so that the average temperature of the temperature measurement resistance elements Al and B 1 and the thin film layer 3 in the vicinity thereof changes depending on the flow velocity. . That is, the series resistance of the resistance temperature elements A 1 and B 1 changes. When this temperature, that is, the series resistance of the resistance temperature measuring elements A 1 and B 1 changes, the resistance of the resistance temperature elements A 1 and B 1 and the thin Along with the thermal delay due to the heat capacity of the membrane layer 3, the temperature change due to the change in the calorific value of the resistance temperature measuring elements A 1 and B 1 interferes with this, resulting in a delay in the response speed. There was a problem.

Summary of the Invention

The present invention has been made to solve the above problems, and has as its object to provide a high-speed response flow rate sensor capable of measuring a wide range of flow rates.

A flow rate sensor according to the present invention includes a base having an air gap, a thin film layer formed on a surface of the base on which the air gap is formed, and a serial connection formed on the thin film layer. A flow rate calculating means for determining a flow velocity of the fluid based on a temperature difference between the first and second resistance temperature resistance elements obtained, and the first and second resistance temperature resistance elements; Control means for controlling the average temperature of the second resistance temperature element to be always higher than the ambient temperature by a constant temperature.

In one configuration example of the flow rate sensor of the present invention, the first and second temperature measuring resistance elements have functions as a heating element and a temperature sensor, and the control means includes first and second temperature measuring resistance elements. This is to control the current flowing through the device.

Further, one configuration example of the flow rate sensor according to the present invention further includes a heating unit disposed near the first and second resistance temperature elements having a function as a temperature sensor, and the control unit supplies the heating unit with the heating unit. The current is controlled.

Further, one configuration example of the flow velocity sensor of the present invention further includes an ambient temperature sensor for measuring an ambient temperature unaffected by the flow of the fluid, and the first and second resistance temperature measuring elements and the ambient temperature sensor are each provided with a bridge circuit. The control means controls the current flowing through the first and second resistance temperature measuring elements so as to keep the voltage difference between the respective middle points of the bridge circuit constant. It is. The apparatus further includes an ambient temperature sensor that measures an ambient temperature unaffected by the flow of the fluid. The first and second resistance temperature measuring elements and the ambient temperature sensor each constitute one side of a bridge circuit. The current flowing to the heating means may be controlled so that the voltage difference between the respective midpoints of the circuit is constant.

Furthermore, at least one voltage follower circuit connected to both ends of the first and second resistance temperature measuring elements is further provided, and the flow rate calculating means is connected in series. The flow velocity is obtained by comparing the divided voltage of the voltage between both ends of the first and second resistance temperature elements and the voltage at the connection point of the first and second resistance temperature elements. . Further, the apparatus further comprises at least one voltage follower circuit connected to both ends of the first and second resistance temperature elements, and the flow rate calculating means includes a first and a second resistance temperature element connected in series. The flow rate may be determined by comparing the divided voltage of the voltage between both ends and the voltage at the connection point of the first and second resistance temperature measuring elements. Further, in one configuration example of the flow rate sensor according to the present invention, the first and second temperature measuring resistance elements are arranged side by side at a predetermined interval in a flowing direction of the fluid in the thin film layer, and generate heat by flowing current. It was made.

Further, one configuration example of the flow rate sensor of the present invention further includes a slit formed on the thin film layer between the first and second resistance temperature elements, and thermally insulating the first and second resistance temperature elements from each other. It is a thing.

In one configuration example of the flow rate sensor of the present invention, the thin film layer is further provided with slits formed at predetermined intervals from each other.

In one configuration example of the flow rate sensor of the present invention, the base includes a diaphragm, and the first and second temperature measurement resistance elements are formed on a surface of the diaphragm opposite to the flow path side, and The calculating means measures the flow velocity of the gas moving on the side of the diaphragm opposite to the side on which the first and second temperature measuring resistance elements are formed. Further, a flow path forming member having a through hole for forming a flow path together with the base is further provided.

The flow velocity calculating means includes a bridge circuit, a differential amplifier circuit, and an output circuit, and the bridge circuit includes a resistor, a first resistance temperature element, and a second resistance element connected in series. The differential amplifier circuit includes a first series circuit, and a second series circuit in which a resistor, a resistor, and an ambient temperature sensor are connected in series. And an operational amplifier connected to the non-inverting input terminal at the connection point between the resistor and the resistor, and the output terminal connected to the connection point between the resistor and the resistor. An operational amplifier connected to the connection point of the first resistance temperature element and having an inverting input terminal and an output terminal connected thereto, one end connected to the output terminal of the operational amplifier, and one end connected to the other end of the resistance And the other end is grounded, A non-inverting input terminal is connected to a connection point between the first resistance temperature element and the second resistance temperature element, and an inverting input terminal is provided with an operational amplifier connected to a connection point between the resistors.

In addition, a flow rate sensor according to the present invention includes a base having an air gap, a thin film layer formed on a surface of the base on which the air gap is formed, and a serial connection formed on the thin film layer. The flow rate of the fluid is determined based on the temperature difference between the first and second resistance temperature elements and the first and second resistance temperature elements, which function as a heating element and a temperature sensor. And a current flowing through the first and second resistance temperature measuring elements so that the average temperature of the first and second resistance temperature elements is always higher than the ambient temperature by a constant temperature. And control means for performing such operations.

Further, a base having a gap, a thin film layer formed on the surface of the base on which the gap is formed, and a temperature sensor formed on the thin film layer and connected in series A first resistance temperature element and a second resistance temperature element having a function; a heating means disposed in the vicinity of the first and second resistance temperature elements; Flow velocity calculating means for calculating the flow velocity of the fluid based on the temperature difference, and controlling the current supplied to the heating means so that the average temperature of the first and second temperature measuring resistance elements is always higher than the ambient temperature by a constant temperature. It is provided with control means for controlling.

BRIEF DESCRIPTION OF THE FIGURES

1A and 1B are a plan view and a sectional view of a flow rate sensor according to a first embodiment of the present invention.

FIG. 2 is an electric circuit diagram of the flow velocity sensor of FIG.

FIG. 3 is a plan view of a flow velocity sensor according to a second embodiment of the present invention.

FIG. 4 is an electric circuit diagram of the flow velocity sensor of FIG.

FIG. 5 is a sectional view of a flow velocity sensor according to a third embodiment of the present invention.

6A and 6B are a plan view and a cross-sectional view of a conventional flow velocity sensor.

FIG. 7 is an electric circuit diagram of a conventional flow velocity sensor.

Detailed description of the embodiment [First embodiment]

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1A is a plan view of a flow velocity sensor according to a first embodiment of the present invention, FIG. 1B is a cross-sectional view taken along the line I-I of FIG. 1A, and FIG. It is a circuit diagram.

The flow rate sensor of the present embodiment is formed on a base 101 made of single-crystal silicon or the like, and a void 102 is formed in the center of the base 101 by, for example, anisotropic etching. Further, on the base 101, a thin film layer (diaphragm member) 103 which is spatially isolated from the base 101 by the gap 102 is formed. Fluid such as gas passes over the thin film layer 103.

The thin film layer 103 is provided with a pair of slits 104 a and 104 b communicating with each other through the gap 102 at a predetermined interval. Further, between these slits 104a and 104b, there is provided a slit 105 extending in a direction perpendicular to a straight line connecting the slits 104a and 104b. Two arranging portions 106a and 106b are formed between the slits 104a and 104b along the flowing direction. The arrangement portions 106a and 106b are thermally insulated from each other by the slit 105.

A temperature measuring resistance element A functioning as a heating element and a temperature sensor is formed in the disposing portion 106a by a thin film forming technique. Similarly, a temperature measuring element functioning as a heating element and a temperature sensor is formed in the disposing portion 106b. Resistive element B is formed by a thin film forming technique. In a portion where the thin film layer 103 and the base 101 are in thermal contact with each other, that is, in a portion where the gap 102 is not provided, the resistance value changes depending on the ambient temperature (temperature of the fluid). Ambient temperature sensor) C is formed by thin film formation technology.

107 and 108 are pads for connecting both ends of the resistance temperature element A to an external electric circuit. Reference numerals 109 and 110 are pads for connecting both ends of the resistance temperature element B to the electric circuit 20. Reference numerals 111 and 112 denote pads for connecting both ends of the ambient temperature resistance measuring element C to the electric circuit 20.

Next, the electric circuit 20 of the flow rate sensor according to the present embodiment will be described with reference to FIG. The electric circuit 20 of the flow rate sensor according to the present embodiment measures the flow rate of the fluid moving on the base 101. And a bridge circuit 21, a differential amplifier circuit (control circuit) 22, and an output circuit 23. The bridge circuit 21 includes a first series circuit in which a resistor R1, a resistance temperature element A and a resistance element B are connected in series, a resistance R2, a resistance R3, and an ambient temperature resistance element C. And a second series circuit connected in series, and is configured by connecting the first series circuit and the second series circuit in parallel.

In the differential amplifier circuit 22, the inverting input terminal is connected to the connection point of the resistor R1 and the resistance thermometer element A, the non-inverting input terminal is connected to the connection point of the resistor R2 and the resistor R3, and the output terminal is It consists of an operational amplifier A1 connected to the connection point of the resistor R1 and the resistor R2.

With such a configuration, the differential amplifier circuit 22 calculates the difference value between the potential V 1 at the connection point between the resistors R 2 and R 3 and the potential V 2 at the connection point between the resistance R 1 and the resistance element A. The amplified output voltage Vo is applied to the connection point between the resistors R1 and R2 of the bridge circuit 21.

The output circuit 23 has an operational amplifier A 2 having a non-inverting input terminal connected to the connection point of the resistor R 1 and the resistance temperature measuring element A, and an inverting input terminal and an output terminal connected thereto, and one end having an operational amplifier A 2. The resistor R5 connected to the output terminal of the resistor R5, one end is connected to the other end of the resistor R5, and the other end is grounded. The operational amplifier A3 is connected to the connection point of the element B, and has an inverting input terminal connected to the connection point of the resistor R5 and the resistor R6.

The balance condition of the bridge circuit 21 is

Resistance value of resistance R 1 Z (resistance value of resistance temperature element A + resistance value of resistance temperature element B) = resistance value of resistance R 2 / (resistance value of resistance R 3 + resistance element of ambient temperature resistance C) Resistance value)

It is. Note that, in this example, at a reference ambient temperature such as room temperature,

The resistance value of the resistor R2 = the resistance value of the resistor R3 + the resistance value of the ambient temperature measuring resistance element C, and

Resistance value of resistance R 1 = (resistance value of resistance element A + resistance value of resistance element B) at the set temperature

It is set to be. Resistance R 3 is the average temperature of resistance temperature elements A and B This is an adjustment resistor to maintain the temperature difference between the temperature and the temperature measurement resistance element C. For the purpose of correcting the temperature characteristics of the flow rate sensor, the temperature difference may not be kept constant, but may be changed, for example, such that this difference increases as the ambient temperature increases.

When a voltage is applied from the operational amplifier A 1 of the differential amplifier circuit 22 to the resistors R 1 and R 2 of the bridge circuit 21, a current flows through the resistance thermometer elements A and B, generating heat. However, when the resistance values of the resistance temperature elements A and B increase and the equilibrium condition is satisfied, the balance is achieved.

Here, when the ambient temperature rises and the resistance value of the ambient temperature measuring resistance element C increases, the bridge circuit 21 loses its balance and the potential V 1 at the connection point between the resistor R 2 and the resistor R 3 is reduced. As the voltage rises, the differential amplifier circuit 22 raises the applied voltage Vo to the bridge circuit 21 in order to rebalance the bridge circuit 21. As a result, the current supplied to the resistance thermometer elements A and B increases, so that the calorific value of the resistance thermometer elements A and B increases, and the resistance values of the resistance thermometer elements A and B increase. Balance occurs where the equilibrium condition is satisfied.

When the ambient temperature decreases and the resistance value of the ambient temperature resistance element C decreases, the potential V1 at the connection point between the resistor R2 and the resistor R3 decreases. 21 Decrease the applied voltage V o to 1. As a result, the calorific values of the resistance temperature elements A and B decrease, the resistance values of the resistance temperature elements A and B decrease, and the balance is established where the above-mentioned equilibrium condition is satisfied.

On the other hand, when a flow velocity occurs in the fluid, the resistance elements A and B are cooled, the resistance values of the resistance elements A and B decrease, and the potential V 2 at the connection point between the resistance R1 and the resistance element A is obtained. , The differential amplifier circuit 22 increases the voltage Vo applied to the bridge circuit 21. As a result, the calorific values of the resistance temperature elements A and B increase, the resistance values of the resistance temperature elements A and B increase, and the balance is established when the above-mentioned equilibrium condition is satisfied.

When the flow velocity decreases and the resistance values of the resistance elements A and B increase, the potential V2 at the connection point between the resistance R1 and the resistance element A increases, so that the differential amplification circuit 2 2 lowers the applied voltage V o to the bridge circuit 21. This allows temperature measurement The calorific value of resistance elements A and B decreases, and the resistance values of resistance temperature elements A and B decrease.

As described above, the differential amplifier circuit 22 detects the temperature detected by the temperature measuring resistance elements A and B (the average value of the temperatures detected by the elements A and B) by the ambient temperature temperature measuring resistance element C. The resistance elements A and B generate heat so that the temperature is always higher than the ambient temperature.

Next, the operational amplifier A2 forms a port follower. The series circuit composed of the resistors R 5 and R 6 is connected to the series circuit composed of the resistance temperature elements A and B via the voltage follower A 2. By using the voltage follower, the current flowing in the bridge circuit 21 is prevented from flowing out to the resistors R5 and R6.

Generally, when the flow velocity is 0, the resistances R 5 and R 6

Resistance value of resistance R5 Z resistance value of resistance R6-resistance value of temperature measuring resistance element A Z resistance value of temperature measuring resistance element B,

Is set to hold. Therefore, when the flow velocity is 0, the potential V 3 at the connection point between the resistance element A and the resistance element B and the potential V 4 at the connection point between the resistance R 5 and the resistance R 6 become the same potential. The output voltage of the operational amplifier A3 becomes zero. Instead of setting as described above, the output voltage when the flow velocity is 0 may be calibrated as the output voltage at the flow velocity 0, or an offset may be set so that the output voltage becomes an arbitrary voltage value when the flow velocity is 0. Good.

As described above, when the flow velocity occurs in the fluid, the resistance temperature elements A and B are cooled. At this time, the resistance element A located upstream is cooled more strongly than the resistance element B located downstream, so that the resistance value of the resistance element A is the resistance of the resistance element B. Value. As a result, the potential V 3 at the connection point between the resistance element A and the resistance element B rises, so that a difference occurs between the potential V 3 and the potential V 4 at the connection point between the resistors R 5 and R 6. . The operational amplifier A 3 outputs an output voltage corresponding to the flow velocity, that is, a voltage proportional to (V 3 −V 4).

As described above, in this embodiment, regardless of the ambient temperature and the flow velocity, the resistance temperature measuring element G. The resistance elements A and B generate heat so that the average value of the temperatures detected at points A and B is always higher than the ambient temperature by a certain amount. When the flow velocity increases, the resistance of the resistance elements A and B increases. The difference in resistance value does not decrease and the sensitivity does not decrease. In this embodiment, a series circuit composed of the resistance temperature elements A and B and a series circuit composed of the resistances R5 and R6 are connected in parallel. Therefore, even if the voltage Vo applied to the bridge circuit 21 changes due to a change in the ambient temperature or the flow velocity, and the voltage V2 changes, the terminal voltage of the resistor R5 (the output voltage of the port-follower A2) is correspondingly changed. ) Also changes to the same value as the voltage V2, so the reference potential (potential V4) of the RTD elements A and B is always adjusted to the value obtained by multiplying the voltage V2 by the predetermined ratio R6Z (R5 + R6). . As a result, the potential difference V3-V4 is a value that reflects only the flow velocity, and a characteristic that increases almost linearly as the flow velocity increases is obtained.

[Second embodiment]

FIG. 3 is a plan view of a flow rate sensor according to a second embodiment of the present invention, and FIG. 4 is an electric circuit diagram of the flow rate sensor of FIG. 3. The same components as those in FIGS. Attach. In the present embodiment, a temperature-measuring resistance element A ′ functioning as a temperature sensor and a heating resistance element D functioning as a heating element are formed in the disposing portion 106a by a thin-film forming technique. Similarly, a temperature measuring resistance element B 'functioning as a temperature sensor and a heating resistance element E functioning as a heating element are formed in the disposition portion 106b by a thin film forming technique.

107 and 108 are pads for connecting both ends of the resistance temperature measuring element A 'to the electric circuit 20a. Reference numerals 109 and 110 denote pads for connecting both ends of the resistance temperature measuring element B 'to the electric circuit 20a. 113 and 114 are pads for connecting both ends of the heating resistance element D to an external electric circuit 20a. 115 and 116 are pads for connecting both ends of the heating resistor element E to the electric circuit 20a.

The bridge circuit 21a of this embodiment uses temperature-measuring resistance elements A 'and B' functioning as temperature sensors instead of the temperature-measuring resistance elements A and B functioning as a heating element and a temperature sensor. In this embodiment, a constant voltage Vs is applied to the connection point between the resistors R1 and R2 of the bridge circuit 21a, and the non-inverting input terminal is connected to the resistor R2 and the resistor R2. The operational amplifier A4 is connected to the connection point of R3 and the inverting input terminal is connected to the connection point of the resistor R1 and the resistance temperature measuring element A '. A heating resistor element D and a heating resistor element E are connected in series to the output terminal of the operational amplifier A4. The operational amplifier A4, the heating resistor element D, and the heating resistor element E form a control circuit 22a.

The balance condition of bridge circuit 21a is

Resistance value of resistance R1 / (resistance value of resistance element A '+ resistance value of resistance element B') = resistance value of resistance R2 / (resistance value of resistance R3 + resistance value of ambient temperature resistance element Mentor C resistance)

It is. When a voltage Vs is applied to the bridge circuit 21a, the operational amplifier A4 generates a potential VI at a connection point between the resistor R2 and the resistor R3 and a potential V at a connection point between the resistor R1 and the resistance temperature measuring element A '. Amplify and output the difference voltage V 1 -V2 from 2.

As a result, a current flows through the heating resistance elements D and E to generate heat. As a result, the temperature of the temperature measuring resistance elements A ′ and B ′ arranged near the heating resistance elements D and E rises. The resistance values of the temperature measurement resistance elements A ′ and B ′ increase and balance occurs where the equilibrium condition is satisfied.

Here, when the ambient temperature rises and the resistance value of the ambient temperature measuring resistance element C increases, the potential VI at the connection point between the resistors R2 and R3 rises, and the operational amplifier A4 outputs the output voltage To rise. As a result, the current supplied to the heating resistor elements D and E increases, so that the amount of heat generated by the heating resistor elements D and E increases, and the resistance values of the temperature measuring resistor elements A ′ and B ′ increase. Balance when the equilibrium condition is satisfied.

When the ambient temperature decreases and the resistance value of the ambient temperature measurement resistance element C decreases, the potential VI at the connection point between the resistor R2 and the resistor R3 decreases, and the operational amplifier A4 decreases the output voltage. . As a result, the amount of heat generated by the heating resistance elements D and E decreases, and the resistance values of the temperature measurement resistance elements A ′ and B ′ decrease, and the balance is established when the above-mentioned equilibrium condition is satisfied.

On the other hand, when a flow velocity occurs in the fluid, the resistance values of the resistance elements A 'and B' decrease, and the potential V2 at the connection point between the resistance R1 and the resistance element A 'decreases. The operational amplifier A4 increases the output voltage. As a result, the amount of heat generated by the heat generating resistance elements D and E increases, and the resistance values of the temperature measuring resistance elements A ′ and B ′ increase.

When the flow velocity decreases and the resistance values of the resistance temperature elements A 'and B' increase, the potential V2 at the connection point between the resistance element 1 and the resistance element A increases, so that the operational amplifier A4 Reduces the output voltage. As a result, the amount of heat generated by the heating resistance elements D and E decreases, the resistance values of the resistance temperature elements A ′ and B ′ decrease, and the balance is established where the equilibrium condition is satisfied.

As described above, the same effects as in the first embodiment can be obtained. Note that the configuration and operation of the output circuit 23a are exactly the same as in the first embodiment.

In the first and second embodiments, the resistance R3 is deleted and the resistance R2 is directly connected to the ambient temperature resistance element C. Instead, the resistance elements A and B (A ', B By adding a resistor in parallel with the series circuit consisting of '), adjustment may be made to maintain the temperature difference between the RTD elements A' and B 'and the ambient temperature RTD element C. In the first and second embodiments, the base 1 made of single-crystal silicon is used. However, a base made of stainless steel, ceramic, sapphire, or the like may be used.

In the first and second embodiments, the average temperature of the two resistance temperature elements connected in series using the bridge circuit and the differential amplifier circuit is calculated from the ambient temperature measured by the ambient temperature resistance element. Although the embodiment in which the temperature is raised by a certain constant has been described, the current is controlled using a microcomputer or the like so that the average temperature of the two temperature measuring resistance elements connected in series is higher than the ambient temperature by a certain temperature. Alternatively, the voltage may be controlled. In other words, the series resistance at the average temperature, which is the setting target of the two temperature measuring resistance elements connected in series, is obtained from the relational expression between temperature and resistance, and the current or voltage applied to achieve the resistance is controlled. May be. In this case, a general external temperature sensor may be used for measuring the ambient temperature. In addition, in FIGS. 1 and 3, the slit 105 may be omitted, and the wiring may be taken out from the middle point of one RTD, so that it may be used as substantially two RTDs. .

[Third embodiment] FIG. 5 is a sectional view of a flow rate sensor according to a third embodiment of the present invention, and the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals. In the first and second embodiments, the elements A, B, and C are provided in the flow of the fluid. However, in the present embodiment, the thin portion (diaphragm portion) 13 3 Elements A, B, and C are provided on the opposite side of the flow path side and not directly in contact with the fluid to be measured.

In FIG. 5, 13 1 is a flow path forming member made of stainless steel, 13 2 is a stainless steel base installed on the flow path forming member 13 1, and 13 3 is a base 13 2 The thin part (diaphragm part) 134 formed on the base 132 is an electrical insulating film such as silicon oxide, silicon nitride, alumina or polyimide. The flow path forming member 13 1 has two through holes 13 7 and 13 8 which form a flow path 13 6 of the fluid. An oval concave portion 135 is formed in the center of the lower surface of the base 132, so that the surface side where the concave portion 135 is formed forms a thin portion (diaphragm portion) 133. The concave portion 135 communicates with the through holes 133 and 138 at both ends. The recesses 135 are preferably oval in order to smoothly flow the fluid, but are not limited to this, and may be rectangular or circular.

On the upper surface of the base 1 32, an electric insulating film 1 34 is formed over the entire surface, and the surface of the electric insulating film 1 34 has temperature-measuring resistance elements A and B and an ambient temperature temperature-measuring resistance element ( : The pads 107 to 112 are formed in the same manner as in the first embodiment.The electric circuit is as shown in Fig. 2. In contrast to the above, the recesses 135 are formed. An electric insulating film is formed on the entire bottom surface, and the temperature measuring resistance elements A and B and the pad are formed in the same manner on the surface of the electric insulating film. It may be formed in the same manner together with the pad via the electric insulating film in the portion, and the fluid may flow on the opposite surface.

Instead of the temperature-measuring resistance elements A and B, the temperature-measuring resistance element C and the pads 107 to 112 of the first embodiment, the temperature-measuring resistance elements A ′ and A ′ of the second embodiment are used. Needless to say, B ′, the ambient temperature resistance element C, the heating resistance elements D and E, and the pads 107 to 116 may be formed. The electric circuit in this case is as shown in FIG. The elements A, B, C, Α,., Β ′, D, における in the first to third embodiments of the present invention are all preferably formed of a platinum thin film or the like. It is not limited to this.

According to the above-described embodiment, the average temperature of the first resistance temperature element and the second temperature resistance element (the average value of the temperatures detected by the first and second resistance temperature elements) is Since the voltage applied to the first resistance temperature element and the second resistance temperature element is controlled such that the temperature is always higher than the ambient temperature by a certain amount, the decrease in sensitivity is reduced even if the flow velocity increases. As a result, a wide range of flow velocities from low to high can be measured. Further, according to the present invention, since the temperatures of the first and second resistance temperature measuring elements can be kept constant, the response speed can be made faster than before. Further, by forming the output circuit from the third series circuit and the differential amplifier, it is possible to extract a value corresponding to the flow velocity of the fluid.

Also, by providing at least one port-difollower connecting the first series circuit and the third series circuit, current flowing in the bridge circuit is prevented from flowing out to the fourth resistor and the fifth resistor. be able to.

As described above, the flow sensor according to the present invention is suitable for measuring a wide range of flow velocities, particularly high flow velocities.

Claims

The scope of the claims

1. a base having an air gap;

A thin film layer formed on a surface of the base on which the gap is formed, a first resistance temperature element and a second temperature measurement element formed on the thin film layer and connected in series; A resistance element;

Flow velocity calculating means for determining a flow velocity of a fluid based on a temperature difference between the first and second temperature measuring resistance elements;

Control means for controlling the average temperature of the first and second temperature measuring resistance elements to be always higher than the ambient temperature by a constant temperature;

A flow rate sensor comprising:

2. The flow sensor according to claim 1,

The first and second temperature measuring resistance elements have functions as a heating element and a temperature sensor,

The flow rate sensor, wherein the control means controls a current flowing through the first and second resistance temperature measuring elements.

3. The flow sensor according to claim 1,

Heating means arranged near the first and second resistance temperature elements having a function as a temperature sensor

Further comprising

The control device controls a current supplied to the heat generating device.

4. In the flow rate sensor according to claim 2,

Further comprising an ambient temperature sensor for measuring an ambient temperature unaffected by the flow of the fluid, the first and second resistance temperature measuring elements, each of the ambient temperature sensors constituting one side of a bridge circuit;

The control means may control the voltage difference at each midpoint of the bridge circuit to be constant.

Controlling the current flowing through the first and second resistance temperature measuring elements Flow rate sensor.

5. The flow sensor according to claim 3,

Further comprising an ambient temperature sensor for measuring an ambient temperature unaffected by the flow of the fluid, wherein the first and second temperature measuring resistance elements each constitute one side of a bridge circuit;

The flow rate sensor according to claim 1, wherein said control means controls a current flowing through said heat generating means so as to keep a voltage difference at each middle point of said bridge circuit constant.

6. The flow sensor according to claim 2,

At least one voltage follower circuit connected to both ends of the first and second resistance temperature elements

Further comprising

The flow velocity calculating means compares a partial voltage of a voltage between both ends of the first and second resistance temperature elements connected in series with a voltage at a connection point of the first and second resistance temperature elements. A flow velocity sensor characterized by determining a flow velocity.

7. The flow sensor according to claim 3,

Further comprising

8. The flow velocity sensor according to claim 1,

The flow rate sensor, wherein the first and second resistance temperature elements are arranged in parallel at a predetermined interval in a flowing direction of the fluid in the thin film layer, and generate heat by a flowing current.

9. The flow velocity sensor according to claim 1,

A slit formed in the thin film layer between the first and second resistance temperature elements to thermally insulate the first and second resistance temperature elements from each other

A flow sensor characterized by further comprising:

10. The flow velocity sensor according to claim 1,

The flow rate sensor according to claim 1, further comprising a slit formed in the thin film layer at a predetermined interval.

1 1. The flow velocity sensor according to claim 1,

The base includes a diaphragm,

The first and second temperature measurement resistance elements are formed on a surface of the diaphragm opposite to the flow path side,

The flow velocity sensor, wherein the flow velocity calculation means measures a flow velocity of a gas moving on a side of the diaphragm opposite to a side on which the first and second resistance temperature elements are formed.

1 2. In the flow rate sensor according to claim 11,

A flow path forming member having a through hole that forms a flow path with the base

A flow rate sensor, further comprising:

1 3. The flow rate sensor according to claim 1,

The flow velocity calculating means includes a bridge circuit, a differential amplifier circuit, and an output circuit.

A first series circuit in which a resistance, the first resistance temperature element, and the second resistance element are connected in series;

A second series circuit in which a resistor, a resistor, and an ambient temperature sensor are connected in series;

With

The differential amplifier circuit,

An inverting input terminal is connected to a connection point between the resistor and the first resistance temperature element, a non-inverting input terminal is connected to a connection point between the resistor and the resistor, and an output terminal is connected to a connection point between the resistor and the resistor. With connected operational amplifier A1,

The output circuit includes:

An operational amplifier having a non-inverting input terminal connected to a connection point between the resistor and the first resistance temperature element, and having an inverting input terminal and an output terminal connected thereto;

A resistor having one end connected to the output terminal of the operational amplifier, one end connected to the other end of the resistor, the other end grounded, and a non-inverting input terminal connected to the first temperature-measuring resistance element. A flow rate sensor comprising: an operational amplifier connected to a connection point between the resistor and the second resistance temperature element, and an inverting input terminal connected to a connection point between the resistance and the resistance.

14. A base having a void portion,

A first thin film layer formed on the surface of the base on which the gap is formed, and a first heating element formed on the thin film layer and having a function as a heating element and a temperature sensor connected in series; A temperature measuring resistance element and a second temperature measuring resistance element; and a flow velocity calculating means for determining a flow velocity of the fluid based on a temperature difference between the first and second temperature measuring resistance elements;

Control means for controlling currents flowing through the first and second resistance temperature elements so that the average temperature of the first and second resistance temperature elements is always higher than the ambient temperature by a constant temperature; and

A flow rate sensor comprising:

15. A base having a void portion,

A thin film layer formed on a surface of the base on which the gap is formed, a first temperature measuring resistor formed on the thin film layer and having a function as a temperature sensor connected in series; An element and a second resistance temperature element;

Heating means arranged in the vicinity of the first and second temperature measuring resistance elements;

Control means for controlling the current supplied to the heat generating means so that the average temperature of the first and second resistance temperature elements is always higher than the ambient temperature by a constant temperature.